1. Field of the Invention
The present invention relates to apparatuses for differentiating blood vessel type in the vascular access field.
2. Prior Art
In medicine numerous vascular access procedures are carried out for placement of needles, catheters, guidewires into blood vessels for a variety of indications and procedures. Arteries and veins are accessed for various and different reasons. Veins are usually accessed for administration of fluids, drugs, blood and blood products, for angiographic studies of the venous system, venous pressure monitoring, blood sampling and others. Arteries are accessed for invasive blood pressure monitoring, delivery of specific drugs at specific locations, angiographic studies, blood sampling for blood gas analysis, interventional cardiological procedures and others.
Except for the superficial suprafascial veins which run alone without the correspondent artery, deep blood vessels, arteries and veins run in most cases alongside with each other, vasa concomitantes, and have the same name. Superficial veins are veins which run above the fascia beneath the skin, return blood from the skin and the subcutaneous regions into the deep veins. In most cases superficial veins are visible under the skin and palpable. These are the veins commonly accessed by health care operators for blood sampling and for placement of intravenous lines.
Deep blood vessels, veins or arteries are anatomically deeply located and are neither visible nor palpable. Deep veins of the systemic circulation are called central veins and are used for vascular access for a variety of indications: rapid administration of fluids, medications, blood or blood product in situation of emergency such as cardiac arrest or shock in which most peripheral veins are collapsed, insertion of cardiac Swan-Ganz balloon catheters, failure to obtain vascular access by the peripheral route, measurement of central vein pressure, insertions of transvenous pacemakers, administration of hyperalimentation solutions and others.
The most common central veins used for gaining access to the circulation are the jugular vein, in the neck, the subclavian vein, beneath the collar bone, and the femoral vein, in the groin.
The procedure for gaining access to central veins and placing a catheter into a central vein is called central line placement. Usually it is carried out with the Seldinger technique which encompasses the insertion of a guidewire into a blood vessel prior to the insertion of a catheter. Regardless of the devices and the techniques used the blood vessel is accessed by the operator via a hollow needle. The operator aims at a target central blood vessel with a needle connected to a syringe or to a Guidewire Placement Device as disclosed by Zadini et al. in U.S. Pat. Nos. 5,415,177, 5,579780 and 5,749,371. Once the operator ascertains blood vessel penetration by visualizing blood flashback into the syringe or the vacuum chamber of the Guidewire Placement Device, the operator proceeds with the Seldinger technique of guidewire insertion. A guidewire is advanced through the hollow needle into the vessel lumen to a desired length. The needle is then removed, the guidewire is left in place within the vessel and a catheter with introducer is slid over the guidewire into the vessel and advanced into it.
Same procedure is carried out for gaining access to arteries.
Due to the fact that arteries and veins run alongside, it is often difficult for the operator to differentiate whether an artery or a vein has been penetrated by the needle tip.
Color of the blood, usually darker in veins, pulsatility of the blood absent in venous blood and present in arterial blood, can help the operator in distinguishing between the two. However no known method or apparatus gives the operator the absolute certainty that a vein has been penetrated instead of an artery.
Placing a catheter in the wrong type of vessel can carry disastrous consequences to a patient, causing significant morbidity and, at times, mortality. Furthermore in carrying out the procedure of central line placement in subclavian or internal jugular veins, the pleura and the lungs can be punctured accidentally by the operator with the needle and the catheter can be erroneously advanced into the pleural cavity. This can result in the dreadful complications of pneumothorax, hemothorax and/or hydrothorax.
It is therefore of paramount importance for the operator "to know where is at with its needle", whether in a vein, artery or pleural cavity, before completing the procedure of guidewire advancement and catheter placement.
Fischell et al. disclose in their U.S. Pat. No. 5,242,414 an "ergonomic vascular access needle" device which allows insertion of a guidewire through a lumen of a plunger of the device into a blood vessel . The device has a centrally located capillary tube in flow communication with a variable volume chamber. The volume of this variable volume chamber can be preset at some specific volumes, different for vein in respect to arteries. When this variable volume chamber is preset for arteries, blood pulsatility can be observed within the capillary tube confirming arterial cannulation instead of venous cannulation as arterial blood within the capillary tube generally pulsates while venous blood generally does not. While this device provide the operator with means of identification of blood vessel type penetration, still has definite drawbacks. First of all, at low pressures, such as pressures encountered often in clinical situations which demand insertion of central lines, the pulsatility of the arterial blood may be absent or hardly distinguishable from variation in length of the blood column which could occur with patient respiration in the venous central system. The method of blood vessel type identification by pulsatility is therefore unreliable as too often unpredictably dependent upon the clinical situation.
Marks discloses in its U.S. Pat. No. 5,314,410 an entry indicator for arterial or intravenous needles. The invention relates to a device basically composed of a hollow needle with transparent hub and a grossly dome shaped membrane with a flexible portion sealingly attached to the inside of the needle hub and covering the proximal portion of the needle. According to the inventor the flexible portion of the membrane may move or inflate in response to pressure within the blood vessel penetrated by the needle tip.
This device has obvious drawbacks and limitations. The device cannot be used with syringes of any type nor guidewire placement devices. Indeed the disclosed device can be used only with catheters over the needle as the membrane attached to the hub and covering the proximal portion of the needle precludes any use of syringes, guidewires, catheters inside the needle as the membrane completely blocks the patency to passageway of the needle.
Furthermore Marks in the cited U.S. Pat. No. 5,314,410 in the paragraph "Background of the invention" states that "the present intravenous and arterial cannulas depend upon a visual observance of blood itself in the hub of the cannula after the blood has flowed trough the length of the cannula in order to indicate that the cannula needle has entered the vessel".
It is obvious that, in the device disclosed by Marks, it is the column of air within the cannula which displaces the flexible portion of the membrane upon blood vessel penetration by the needle tip serving as indicator of blood vessel penetration. Otherwise, should be the blood to deflect the flexible portion of the membrane, the device would be neither useful nor novel as the operator would visualize the blood at the proximal end of the needle well before the flexible portion of the membrane flexes in response to the fluid pressure of the blood.
It is seems obvious that the column of air, capable of stretching the flexible portion of the membrane to the extent disclosed, illustrated and claimed in the Mark's Patent requires a certain degree of compression prior to the stretching of the flexible portion of the membrane. This compression of air may delays the indication of blood vessel penetration by the needle tip and may make Mark's device unreliable in clinical situations of low blood pressure where the column of air is expected to be only marginally compressed.
A search in the Patent office failed to identify any apparatus for syringes or guidewires placement devices or in general for vascular access devices provided with vacuum creating means, capable of achieving blood vessel type differentiation rapidly, swiftly and reliably at bedside as the invention below disclosed.